The development of massively parallel sequencing technologies may hold the key to personalized medicine as it allows for the identification of functional genetic variants that rende a person susceptible to disease. For this to become reality, disease-causing genes must be identified. This proposal concentrates on non-syndromic congenital heart defects (CHDs). Representing the most common type of birth defect, CHDs affect not only children but also a growing population of adult survivors. Epidemiologic studies have demonstrated genetic contributors, but few etiologic genes have been identified. Until this knowledge gap is overcome, the underlying molecular cause will remain hidden and hinder the development of new therapies and potentially prediction of long-term complications. Our long-term goal is to identify the underlying genetic causes and elucidate the molecular mechanisms leading to CHDs. The overall objective of this application is to discover the genetic variation that results in CHDs. Th central hypothesis is that CHD-causing genes can be identified by a genome-wide sequencing approach, using families exhibiting Mendelian inheritance patterns. The rationale for the proposed research is that the discovery of genetic causes of CHDs has the potential to provide better risk counseling and result in novel therapies for malformations that contribute to mortality from infancy to adulthood. Guided by recent literature supporting this premise and possession of a unique cohort of families, the central hypothesis will be tested by pursuing two Specific Aims: 1) Expand our current cohort of multiplex families and sporadic cases of CHDs; 2) Identify disease-causing genes in families exhibiting Mendelian segregation for CHDs and in trios via transmission disequilibrium tests by exome and whole genome sequencing. Methods will be developed specifically to test for rare variant associations in trio data, which aggregate over variants within a gene region and weight these variants based upon frequency and functionality. These methods will also allow for the joint analysis of unrelated individuals with a family history of CHD and trio data. The putative causal variants functional effects will be investigated by in vitro and in vivo Xenopus assays. A larger cohort with CHD will then be screened for mutations in identified genes. Our approach is innovative not only because it employs new technologies but also adds the power of Mendelian genetics through the use of families to tackle the genetic basis of a complex disease. This application focuses on part of the NHLBI Strategic Plan goals and challenges to identify key genetic variants in the human population that are associated with specific diseases. Success of this proposal will create a paradigm shift in the approach for human disease gene identification. The proposed research is significant because it is expected to vertically advance the fields of human genetics, developmental biology and cardiovascular medicine by identifying causal genes for CHDs. In the current era of fetal diagnosis and intervention, this knowledge will be used to improve prevention measures, in utero diagnosis, genetic counseling and therapy.